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Al2O3 Based Hybrid Composites
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 4 (2017) 10870–10878
www.materialstoday.com/proceedings
AMMMT 2016
Influence of Heat Treatment on Corrosion Resistance of A356/RHA/Al2O3 Based Hybrid Composites a
a
b
Hanumanthe Gowda , P. Rajendra Prasad ,
Department of Mechanical Engineering , R.L.Jalappa Institute of Technology, Doddaballapur, Bangalore Rural Dist. , Karnataka. b
Yadavrao Tasgaonkar Institute of Engineering and Technology, Tal. Karjat, Dist. Raigad
Abstract Aluminium metal matrix composites (MMC’s) have gained importance in various industries because of their good mechanical and tribological properties such as high strength, low density, wear and corrosion resistance and good structural rigidity. Aluminium MMC’s are preferred in the fields of marine, aerospace, military and in many other domestic applications. In this study it is intended to develop and study the corrosion resistance of A356/RHA/Al2O3 reinforced hybrid aluminium metal matrix composites. The composite is prepared by using liquid metallurgy route (Stir casting technique) and liquid state has some important advantages such as better matrix particle bonding, easier control of matrix structure, Simplicity, low cost of processing, nearer to next shape and wide selection of material.A356 alloy is taken as the base matrix to which Al2O3 and RHA particulates in equal proportions (1Wt%,2Wt%,3Wt%,4Wt% &5Wt%) are used as reinforcements and corrosion resistance of prepared hybrid composites with aging conditions were examined. A scope of enhancement in corrosion resistance is observed in Double aged with strain specimens over as-cast, single aged and double aged without strain condition. It was also observed that the density of hybrid composites decreased with increasing particle content. © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of Advanced Materials, Manufacturing, Management and Thermal Science (AMMMT 2016). Keywords: Rice Husk Ash (RHA), Hybrid composites, A356, Stir Casting.
1. Introduction The structural material that is composed of two or more combined constituents is known as composite and those combined constituents are mixed at a macroscopic level and are not soluble in each other. One constituent chosen is * Corresponding author. Tel.: +91 9611393057 E-mail address: [email protected] 2214-7853© 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of Advanced Materials, Manufacturing, Management and Thermal Science (AMMMT 2016).
Hanumanthe Gowda,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
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known as the reinforcing phase and the one in which it is embedded is called the matrix phase. The reinforcing phase material may be in the form of fibers, particles or flakes. The matrix phase materials are normally continuous. Composite materials are new generation materials developed to meet the demands of rapid development of technological changes of the industry [1-4].Shenoy H et al., [5] have described in their work that the resistance to corrosion of Al 6061-Mica/E-glass fiber can be improved by heat treatment in an effective manner. Dasappa R et al., [6] Studied that the corrosion resistance of the material can be improved by the frit inclusion in Al 6061 matrix. Metal matrix composites (MMC’s) progressively adapt as an appealing material for advanced Aerospace, Automotive and Marine hardware applications. The properties of MMC’s can be modified by adding the preferred reinforcement. The parameters of micro-structural reinforcement are the size and shape of material, weight fractions of reinforcements and as well as orientation and distribution. Thus, the elastic properties of the MMC’s are greatly determined by its micro-structural parameters of the reinforcement [7]. Various light metals such as Aluminium, Magnesium and many more are being used as matrices, among these light metals, especially aluminium and alloys of aluminium are being used much extensively in manufacturing of MMC’s as matrices. The Aluminium metal matrix composites show numerous exceptional mechanical and superior wear resistance characteristics in comparison with the matrix alloy. Due to this factor the current investing applications are considering MMC’s which are based on aluminium alloy and these MMC’s are being proposed as aspirant materials [8]. A huge number of researchers analyzed that production of discontinuous reinforced metal matrix composites can be made economical by adopting the melting and casting techniques. The related works on metal matrix composites demonstrated that there is no much published data available on production techniques of A356/RHA/ Al2O3 hybrid metal matrix composites with corrosion behavior. 2. Aim of the present work In the present work an attempt is made to develop an A356 Alloy based hybrid composites with the use of RHA and Al2O3 particulates of equal proportions (1wt%, 2wt%, 3wt%, 4wt% and 5wt %) with an end application in marine filed. This hybrid composite is used to manufacture the external portion of the ship that is immersed continuously in a sea water always. The immersed part should be hard and resistant to corrosion. 3. Material selection Khanna O.P (2007) published that, while selecting a suitable material for experimental process several factors needs to be considered, such as service, fabrication, and economic requirements. The materials such as i) A356 ii) RHA iii) Al2O3 has been selected based on the comprehensive survey done in literature. RHA and Al2O3 are reinforcements whereas A356 is a matrix material. 3.1. Al2O3 The Al2O3 supplied by Vasa Scientific Co, in the form of a powder of average particle size 100ìm.The density of Al2O3 used is 3.69 g/cc. 3.2. Aluminium356 M. Abdulwahab et al. (2012) have noted that A356 possess high strength, superior casting properties, heat treatment capability. Due to these properties and its wide applications, A356 was chosen as a matrix material which is available in the form of ingots. The A356 chemical composition applied in the present experimental study is represented in the Table-1.The density of A356 used is 2.67 g/cc.
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Hanumanthe Gowda.,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
Table -1: A356 Chemical composition Element
Weight%
Si
6.6
Mg
0.45
Fe
0.10
Ti
0.10
Cu
0.05
Mn
0.055
Zn
0.005
Ni
0.005
Al
Balance
3.3. RHA (Rice Husk Ash) Siva Prasad et al. [9] concluded that most economical and low density material is rice husk ash (RHA). The RHA is available as a byproduct in huge quantities as a reinforcement material. Rice husk obtained as a byproduct after rice milling procedure and this is agriculture debris. Rice husk consists of 20% inorganic substances and rest is the organic substances. After rice milling the 50kg of rice, it is approximated that, rice husk of 10Kg can be obtained. When we burn the rice husk, the RHA is acquired. To enhance the mechanical properties as well as to lower the material density, here RHA, which is of less weight and available in surplus, is being used as reinforcement in MMC’s. The chemical composition of RHA used is as presented in Table-2. An average granular size of RHA is 75ìm.The mass density of RHA used is 2.1 g/cc. Table-2: The RHA chemical composition Element
Weight%
Silica
90.23
Graphite
4.77
Calcium oxide
1.58
Magnesium Oxide
0.53
Potassium oxide
0.39
Ferric Oxide
0.21
4. Experimental work The rice husk was burned and the ash obtained was intensively cleaned with H2O to discard fine particles and dehydrated at normal room temperature for 1day. Cleaned rice husk ash was then heated at 200ºC for 60min in order to eliminate the organic matter and wateriness. The resulted material is then kept for heating at 600ºC for about 12hr. This process removes the carbonaceous material [10]. After this process, the color of the material changes to grayish white from its original color of black. Thus, in the preparation of composites, the reinforcement material used is a silica-rich ash obtained from the above process. The Stir casting is a type of liquid metallurgy technique method. This method has advantages like production cost is less; control of material is an easy and discontinuous reinforcement of casting ingots uses this method. There are various other techniques like liquid metallurgy technique, Powder metallurgy, and spray deposition, etc., were feasible to formulate the MMC’s. However, Stir casting is advantageous over the all available techniques. The mechanical properties of the resulting composite materials after the reinforcement of RHA and Al2O3 can be studied by carrying out several experiments and results can be analyzed to discover the reinforcement effects.
Hanumanthe Gowda,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
10873
A356 aluminium alloy was charged in the electric furnace and superheated to a temperature of 800°C.The stir casting technique was used to fabricate specimens and after applying this method, the melt of the matrix alloy creates the vortex. The stainless steel stirrer puts into the melt and stirred at the speed of 500RPM slowly to mix the molten metal. The reinforcement particles, RHA and Al2O3 were preheated to 450°C for 1h. After preheating, particles are consolidated it into the melt to exclude moisture. To reduce the porosity, the addition of the degassing tablet has been done once after the metal is completed melted. To enrich the wettability, meantime 1% by weight of magnesium was included in the melt. This addition of magnesium improves the wettability between the matrix alloy and the reinforcement. The preheated particles of RHA and Al2O3 were included during constantly stirring of molten metal. Even after the accomplishment of particle feeding, the stirring was preceded for another 5-10 min. After this stage, the molten mixture was drained into the mould. To accomplish the uniform solidification of the molten metal the mould was preheated to 200°C for 30min. Thus, particle strengthened hybrid composite materials are formed by adapting the stir casting process and 1%, 2%, 3%, 4% and 5 % by equal weight proportions of RHA and Al2O3 are thus used. 4.1. Heat Treatment Procedure The following steps are involved in the heat treatment procedure: • • • •
Solutionizing Quenching Stretching/straining Aging
○ ○
Aging with low temperature (Single aging) Aging at higher temperature(Double aging)
• Solutionizing and Quenching: The solution treatment is done for two hours, first soaking temperature of 540°C was maintained succeeded by water quench at room temperature was carried out. • Stretching/straining: This is a particular condition where, instantaneously after the heat treatment and quenching, before precipitation starts and the hybrid composite material become harder. An external force is applied (before 5Hrs) to permanently deform the one set of prepared samples by 8 % to 10 %. • Single aging: After quenching single aging is at the temperature of 140°C for about 12hrs of period is carried out. • Double aging: The Second step of aging procedure also done for the 12hrsof time and at a temperature of 190°C. 5. Results and discussion The samples were machined as per the ASTM specifications and were exposed to solution heat treatment. Density and Corrosion resistance of formed hybrid composites have been analyzed. 5.1. Microstructure Analysis The microstructure examination confirms the presence of the reinforcements inside the composites. Once the casting is ready, a cross section sample was collected from the castings. These castings are carrying through grinding at the beginning and then emery paper was used to polish the ground one, at last, engraved using Keller’s solution and was examined through an optical microscope. The optical microscope has been used to investigate the A356 alloy based hybrid composite material.The Aluminium composites which are reinforced with RHA and Al2O3 particulate and microstructures obtained from optical microscope are shown from Fig.1 to Fig. 4.
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Hanumanthe Gowda.,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
Fig. 1: Microstructure of As-cast A356 Hybrid composite (4% RHA and 4% Al2O3)
Fig. 2: Microstructure of Single aged A356 Hybrid composite (4%RHA and 4% Al2O3)
Fig. 3: Microstructure of Double aged without strain A356 Hybrid composite (4%RHA and 4% Al2O3)
Fig. 4: Microstructure of Double aged with strain A356 Hybrid composite (4%RHA and 4% Al2O3).
The optical micrographs demonstrate the uniform distribution of RHA and Al2O3 reinforcement particles in the matrix. And it is evident that there are no voids and discontinuities in the A356 alloy composite material. Thus, we can say that the good interfacial bonding among the reinforcement particles and matrix material.
Hanumanthe Gowda,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
5.2.
10875
Density Measurement
Fig. 5: Density of A356 alloy hybrid composite by Archimedes Principle
Archimedes Principle can be used to measure the density. From Fig. 5 we can observe that density of A356 Alloy Hybrid composite material reduces when the percentage of reinforcement RHA and Al2O3 increases. The presence of voids in matrix, low interface bonding between reinforcement and matrix and development of fracture of reinforcement leads to lower density with increase in reinforcement. The presence of higher porosity may be due to solidification nature and due to the agglomeration of Al2O3 [11]. The Archimedes Principle can be applied here and the succeeding expression can be derived for the density of the composites.
Where m is the mass of the composite specimen in air, m1 is the mass of the same composite specimen in distilled water and ρw is the density of distilled water. The density of distilled water at 20°C is 998Kg/m3. 5.3. Corrosion Test Various solutions were prepared and stored in vessels; by dipping the samples in these vessels corrosion test was performed. The solution is prepared using 5% NaCl , Sea Water and 0.1 normal HCL and the samples were soaked in to it for a period of 96 hours. After this the specimens are cleaned with H2O and rinsed with acetone and weight is checked in an electronic weighing machine. Following formula can be used to calculate the percentage of corrosion rate.
Where, Wi is the initial weight before corrosion and W a is the final weight after corrosion.
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Fig. 6: Evaluation of corrosion rate for specimens with different RHA and Al2O3 particulates with Aging conditions in 0.1 normal HCL
Fig. 7: Evaluation of corrosion rate for specimens with different RHA and Al2O3 particulates with Aging conditions in 5% NaCl
Fig. 8: Evaluation of corrosion rate for specimens with different RHA and Al2O3 particulates with Aging conditions in Sea water.
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From the Fig. 6, 7 and 8, it is noticeable that the corrosion rate of the A356 hybrid composite material is much lower when compared to that of its parent metal. With the increases in wt% of RHA and Al2O3 content the corrosion resistance has improved. This is due to the inclusion of reinforcement makes the A356 alloy into stronger and resistant to corrosion. And stabilized material has been resulted from the heat treatment and aging and hence there is an appreciable reduction in corrosion resistance. It is also evidence that the corrosion rate in NaCl and sea water is lesser than HCL. 6. Conclusion This study, conducted on A356 based hybrid composites materials with RHA and Al2O3 particulates as reinforcement materials with as-cast and various aging conditions the preceding conclusions can be made. •
To fabricate the hybrid composite material of the A356 alloy matrix we can use the stir casting method and the particles of RHA and Al2O3 can be effectively added to the A356.
•
When there is an increase in RHA and Al2O3 particulates percentage in the alloy matrix, then the density of A356 alloy based hybrid composites decreases.
•
It is evidenced that corrosion loss decreased with increase in RHA and Al2O3 particles in the matrix alloy under different test conditions. Thus the corrosion resistance of the hybrid composites is highly influenced by the heat treatment.
•
The outcomes captured evidently demonstrate that the double aged with strain specimens shown improved corrosion resistance in comparison with the single aging and as cast specimens.
•
It is clearly demonstrated that composites with 4% of RHA and Al2O3 particles have shown improved corrosion resistance in comparison with the other combinations.
•
Further increase in reinforcement did not show significant improvement because of reinforcement floating on the metal and removed as dross.
Acknowledgement My Sincere thanks are due to my supervisor Dr. P. Rajendra Prasad, for the valuable guidance offered during every stage of my research work. I thank Principal, RLJIT and the management of R. L. Jalappa Institute of technology for the support, encouragement and facilities provided at the institute. References [1] [2] [3] [4] [5] [6]
[7] [8]
Phrahakar kammer et al,2012,Experimental studies on mechnacial properties of E-glass short fibers and fly ash reinforced Al7075 hybrid metal matrix composites” ,International journal of mechanical and industrial engoneering, Vol-1,Issue 4,pp111-115. Ramesh D et al. 2012, “Sand abrasive behavior of aluminium –frit particulate metal matrix composites”,International journal of emrging trends in engineering and development,Vol 5,Issue 2,pp231-237. Ghanashyam H et al. 2012, “Evalaution of wear and hardness of Al-Si-Mg based hybrid composite at different aging conditions”,Internattional journal of scientific and research publications,Vol 2,Issue 8,pp-1-7 Honnaiah C et al, 2014, “Effect of particle size on dry sliding wear of cast A356-Al₂O₃ Metal matrix composites, International journal of engineering trends and Technology”, Vol 12, pp 438-445. Shenoy H et al ,2013 ”Evaluation of ultimate tensile strength and corrosion resistance of Al-Mg-Si based hybrid composite in different ageing condition”, International Journal of material science, Vol 8, pp 29-37. Dasappa R et al,2013,”Corrosion behaviour of Al6061-frit particulate metal matrix composits in sodium chloride solution”,Journals of minerals and materials characterization and engineering,Vol 1,pp 15-19. Madeva nagaral et al. 2013, “ Mechnacial bevaviour of aluminium 6061alloy reinforced with Al2O3 and Graphite particulate hybrid metal matrix composites”,International journal of research in engineering and technology,Vol 1,Issue 2,pp 193-198. M. Sreenivasa Reddy et al, 2014 “Influence of reinforcement and heat treatment on mechanical and wear properties of Al 7075 based hybrid composite”, International conference on advances in manufacturing and materials engineering, pp 508-516.
10878 [9]
Hanumanthe Gowda.,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
D.Shiva prasad et al,2011“Production and mechanical properties of A356.2/RHA composites”, International journal of advanced science and technology, vol33, pp51-57.
[10] Chintada shoba et al, 2014, ’’Investigation on mechanical properties of aluminium hybrid composites’’, Journal of materials research and technology(jmr&t), Vol 3, pp 79-85. [11] Vignesh v et al.2104, “Fabrication,surface morphology and corrosion investigation of Al 7075- Al2O3 matrix compsote in sea water and th industrial environment”, 12 Global congress on manufacturing and management,pp 607-613. [12] Khanaa O P, 2007 “Material Science and Metallurgy”, Dhanpat Rai Publications, pp2-4. [13] M. Abdulwahab et al, 2012 “Effect of thermal ageing treatment on the mechanical properties of antimony modified, Al356-type Al-Si-Mg alloy”, JMES, pp 87-92.
ScienceDirect Materials Today: Proceedings 4 (2017) 10870–10878
www.materialstoday.com/proceedings
AMMMT 2016
Influence of Heat Treatment on Corrosion Resistance of A356/RHA/Al2O3 Based Hybrid Composites a
a
b
Hanumanthe Gowda , P. Rajendra Prasad ,
Department of Mechanical Engineering , R.L.Jalappa Institute of Technology, Doddaballapur, Bangalore Rural Dist. , Karnataka. b
Yadavrao Tasgaonkar Institute of Engineering and Technology, Tal. Karjat, Dist. Raigad
Abstract Aluminium metal matrix composites (MMC’s) have gained importance in various industries because of their good mechanical and tribological properties such as high strength, low density, wear and corrosion resistance and good structural rigidity. Aluminium MMC’s are preferred in the fields of marine, aerospace, military and in many other domestic applications. In this study it is intended to develop and study the corrosion resistance of A356/RHA/Al2O3 reinforced hybrid aluminium metal matrix composites. The composite is prepared by using liquid metallurgy route (Stir casting technique) and liquid state has some important advantages such as better matrix particle bonding, easier control of matrix structure, Simplicity, low cost of processing, nearer to next shape and wide selection of material.A356 alloy is taken as the base matrix to which Al2O3 and RHA particulates in equal proportions (1Wt%,2Wt%,3Wt%,4Wt% &5Wt%) are used as reinforcements and corrosion resistance of prepared hybrid composites with aging conditions were examined. A scope of enhancement in corrosion resistance is observed in Double aged with strain specimens over as-cast, single aged and double aged without strain condition. It was also observed that the density of hybrid composites decreased with increasing particle content. © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of Advanced Materials, Manufacturing, Management and Thermal Science (AMMMT 2016). Keywords: Rice Husk Ash (RHA), Hybrid composites, A356, Stir Casting.
1. Introduction The structural material that is composed of two or more combined constituents is known as composite and those combined constituents are mixed at a macroscopic level and are not soluble in each other. One constituent chosen is * Corresponding author. Tel.: +91 9611393057 E-mail address: [email protected] 2214-7853© 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of Advanced Materials, Manufacturing, Management and Thermal Science (AMMMT 2016).
Hanumanthe Gowda,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
10871
known as the reinforcing phase and the one in which it is embedded is called the matrix phase. The reinforcing phase material may be in the form of fibers, particles or flakes. The matrix phase materials are normally continuous. Composite materials are new generation materials developed to meet the demands of rapid development of technological changes of the industry [1-4].Shenoy H et al., [5] have described in their work that the resistance to corrosion of Al 6061-Mica/E-glass fiber can be improved by heat treatment in an effective manner. Dasappa R et al., [6] Studied that the corrosion resistance of the material can be improved by the frit inclusion in Al 6061 matrix. Metal matrix composites (MMC’s) progressively adapt as an appealing material for advanced Aerospace, Automotive and Marine hardware applications. The properties of MMC’s can be modified by adding the preferred reinforcement. The parameters of micro-structural reinforcement are the size and shape of material, weight fractions of reinforcements and as well as orientation and distribution. Thus, the elastic properties of the MMC’s are greatly determined by its micro-structural parameters of the reinforcement [7]. Various light metals such as Aluminium, Magnesium and many more are being used as matrices, among these light metals, especially aluminium and alloys of aluminium are being used much extensively in manufacturing of MMC’s as matrices. The Aluminium metal matrix composites show numerous exceptional mechanical and superior wear resistance characteristics in comparison with the matrix alloy. Due to this factor the current investing applications are considering MMC’s which are based on aluminium alloy and these MMC’s are being proposed as aspirant materials [8]. A huge number of researchers analyzed that production of discontinuous reinforced metal matrix composites can be made economical by adopting the melting and casting techniques. The related works on metal matrix composites demonstrated that there is no much published data available on production techniques of A356/RHA/ Al2O3 hybrid metal matrix composites with corrosion behavior. 2. Aim of the present work In the present work an attempt is made to develop an A356 Alloy based hybrid composites with the use of RHA and Al2O3 particulates of equal proportions (1wt%, 2wt%, 3wt%, 4wt% and 5wt %) with an end application in marine filed. This hybrid composite is used to manufacture the external portion of the ship that is immersed continuously in a sea water always. The immersed part should be hard and resistant to corrosion. 3. Material selection Khanna O.P (2007) published that, while selecting a suitable material for experimental process several factors needs to be considered, such as service, fabrication, and economic requirements. The materials such as i) A356 ii) RHA iii) Al2O3 has been selected based on the comprehensive survey done in literature. RHA and Al2O3 are reinforcements whereas A356 is a matrix material. 3.1. Al2O3 The Al2O3 supplied by Vasa Scientific Co, in the form of a powder of average particle size 100ìm.The density of Al2O3 used is 3.69 g/cc. 3.2. Aluminium356 M. Abdulwahab et al. (2012) have noted that A356 possess high strength, superior casting properties, heat treatment capability. Due to these properties and its wide applications, A356 was chosen as a matrix material which is available in the form of ingots. The A356 chemical composition applied in the present experimental study is represented in the Table-1.The density of A356 used is 2.67 g/cc.
10872
Hanumanthe Gowda.,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
Table -1: A356 Chemical composition Element
Weight%
Si
6.6
Mg
0.45
Fe
0.10
Ti
0.10
Cu
0.05
Mn
0.055
Zn
0.005
Ni
0.005
Al
Balance
3.3. RHA (Rice Husk Ash) Siva Prasad et al. [9] concluded that most economical and low density material is rice husk ash (RHA). The RHA is available as a byproduct in huge quantities as a reinforcement material. Rice husk obtained as a byproduct after rice milling procedure and this is agriculture debris. Rice husk consists of 20% inorganic substances and rest is the organic substances. After rice milling the 50kg of rice, it is approximated that, rice husk of 10Kg can be obtained. When we burn the rice husk, the RHA is acquired. To enhance the mechanical properties as well as to lower the material density, here RHA, which is of less weight and available in surplus, is being used as reinforcement in MMC’s. The chemical composition of RHA used is as presented in Table-2. An average granular size of RHA is 75ìm.The mass density of RHA used is 2.1 g/cc. Table-2: The RHA chemical composition Element
Weight%
Silica
90.23
Graphite
4.77
Calcium oxide
1.58
Magnesium Oxide
0.53
Potassium oxide
0.39
Ferric Oxide
0.21
4. Experimental work The rice husk was burned and the ash obtained was intensively cleaned with H2O to discard fine particles and dehydrated at normal room temperature for 1day. Cleaned rice husk ash was then heated at 200ºC for 60min in order to eliminate the organic matter and wateriness. The resulted material is then kept for heating at 600ºC for about 12hr. This process removes the carbonaceous material [10]. After this process, the color of the material changes to grayish white from its original color of black. Thus, in the preparation of composites, the reinforcement material used is a silica-rich ash obtained from the above process. The Stir casting is a type of liquid metallurgy technique method. This method has advantages like production cost is less; control of material is an easy and discontinuous reinforcement of casting ingots uses this method. There are various other techniques like liquid metallurgy technique, Powder metallurgy, and spray deposition, etc., were feasible to formulate the MMC’s. However, Stir casting is advantageous over the all available techniques. The mechanical properties of the resulting composite materials after the reinforcement of RHA and Al2O3 can be studied by carrying out several experiments and results can be analyzed to discover the reinforcement effects.
Hanumanthe Gowda,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
10873
A356 aluminium alloy was charged in the electric furnace and superheated to a temperature of 800°C.The stir casting technique was used to fabricate specimens and after applying this method, the melt of the matrix alloy creates the vortex. The stainless steel stirrer puts into the melt and stirred at the speed of 500RPM slowly to mix the molten metal. The reinforcement particles, RHA and Al2O3 were preheated to 450°C for 1h. After preheating, particles are consolidated it into the melt to exclude moisture. To reduce the porosity, the addition of the degassing tablet has been done once after the metal is completed melted. To enrich the wettability, meantime 1% by weight of magnesium was included in the melt. This addition of magnesium improves the wettability between the matrix alloy and the reinforcement. The preheated particles of RHA and Al2O3 were included during constantly stirring of molten metal. Even after the accomplishment of particle feeding, the stirring was preceded for another 5-10 min. After this stage, the molten mixture was drained into the mould. To accomplish the uniform solidification of the molten metal the mould was preheated to 200°C for 30min. Thus, particle strengthened hybrid composite materials are formed by adapting the stir casting process and 1%, 2%, 3%, 4% and 5 % by equal weight proportions of RHA and Al2O3 are thus used. 4.1. Heat Treatment Procedure The following steps are involved in the heat treatment procedure: • • • •
Solutionizing Quenching Stretching/straining Aging
○ ○
Aging with low temperature (Single aging) Aging at higher temperature(Double aging)
• Solutionizing and Quenching: The solution treatment is done for two hours, first soaking temperature of 540°C was maintained succeeded by water quench at room temperature was carried out. • Stretching/straining: This is a particular condition where, instantaneously after the heat treatment and quenching, before precipitation starts and the hybrid composite material become harder. An external force is applied (before 5Hrs) to permanently deform the one set of prepared samples by 8 % to 10 %. • Single aging: After quenching single aging is at the temperature of 140°C for about 12hrs of period is carried out. • Double aging: The Second step of aging procedure also done for the 12hrsof time and at a temperature of 190°C. 5. Results and discussion The samples were machined as per the ASTM specifications and were exposed to solution heat treatment. Density and Corrosion resistance of formed hybrid composites have been analyzed. 5.1. Microstructure Analysis The microstructure examination confirms the presence of the reinforcements inside the composites. Once the casting is ready, a cross section sample was collected from the castings. These castings are carrying through grinding at the beginning and then emery paper was used to polish the ground one, at last, engraved using Keller’s solution and was examined through an optical microscope. The optical microscope has been used to investigate the A356 alloy based hybrid composite material.The Aluminium composites which are reinforced with RHA and Al2O3 particulate and microstructures obtained from optical microscope are shown from Fig.1 to Fig. 4.
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Hanumanthe Gowda.,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
Fig. 1: Microstructure of As-cast A356 Hybrid composite (4% RHA and 4% Al2O3)
Fig. 2: Microstructure of Single aged A356 Hybrid composite (4%RHA and 4% Al2O3)
Fig. 3: Microstructure of Double aged without strain A356 Hybrid composite (4%RHA and 4% Al2O3)
Fig. 4: Microstructure of Double aged with strain A356 Hybrid composite (4%RHA and 4% Al2O3).
The optical micrographs demonstrate the uniform distribution of RHA and Al2O3 reinforcement particles in the matrix. And it is evident that there are no voids and discontinuities in the A356 alloy composite material. Thus, we can say that the good interfacial bonding among the reinforcement particles and matrix material.
Hanumanthe Gowda,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
5.2.
10875
Density Measurement
Fig. 5: Density of A356 alloy hybrid composite by Archimedes Principle
Archimedes Principle can be used to measure the density. From Fig. 5 we can observe that density of A356 Alloy Hybrid composite material reduces when the percentage of reinforcement RHA and Al2O3 increases. The presence of voids in matrix, low interface bonding between reinforcement and matrix and development of fracture of reinforcement leads to lower density with increase in reinforcement. The presence of higher porosity may be due to solidification nature and due to the agglomeration of Al2O3 [11]. The Archimedes Principle can be applied here and the succeeding expression can be derived for the density of the composites.
Where m is the mass of the composite specimen in air, m1 is the mass of the same composite specimen in distilled water and ρw is the density of distilled water. The density of distilled water at 20°C is 998Kg/m3. 5.3. Corrosion Test Various solutions were prepared and stored in vessels; by dipping the samples in these vessels corrosion test was performed. The solution is prepared using 5% NaCl , Sea Water and 0.1 normal HCL and the samples were soaked in to it for a period of 96 hours. After this the specimens are cleaned with H2O and rinsed with acetone and weight is checked in an electronic weighing machine. Following formula can be used to calculate the percentage of corrosion rate.
Where, Wi is the initial weight before corrosion and W a is the final weight after corrosion.
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Fig. 6: Evaluation of corrosion rate for specimens with different RHA and Al2O3 particulates with Aging conditions in 0.1 normal HCL
Fig. 7: Evaluation of corrosion rate for specimens with different RHA and Al2O3 particulates with Aging conditions in 5% NaCl
Fig. 8: Evaluation of corrosion rate for specimens with different RHA and Al2O3 particulates with Aging conditions in Sea water.
Hanumanthe Gowda,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
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From the Fig. 6, 7 and 8, it is noticeable that the corrosion rate of the A356 hybrid composite material is much lower when compared to that of its parent metal. With the increases in wt% of RHA and Al2O3 content the corrosion resistance has improved. This is due to the inclusion of reinforcement makes the A356 alloy into stronger and resistant to corrosion. And stabilized material has been resulted from the heat treatment and aging and hence there is an appreciable reduction in corrosion resistance. It is also evidence that the corrosion rate in NaCl and sea water is lesser than HCL. 6. Conclusion This study, conducted on A356 based hybrid composites materials with RHA and Al2O3 particulates as reinforcement materials with as-cast and various aging conditions the preceding conclusions can be made. •
To fabricate the hybrid composite material of the A356 alloy matrix we can use the stir casting method and the particles of RHA and Al2O3 can be effectively added to the A356.
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When there is an increase in RHA and Al2O3 particulates percentage in the alloy matrix, then the density of A356 alloy based hybrid composites decreases.
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It is evidenced that corrosion loss decreased with increase in RHA and Al2O3 particles in the matrix alloy under different test conditions. Thus the corrosion resistance of the hybrid composites is highly influenced by the heat treatment.
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The outcomes captured evidently demonstrate that the double aged with strain specimens shown improved corrosion resistance in comparison with the single aging and as cast specimens.
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It is clearly demonstrated that composites with 4% of RHA and Al2O3 particles have shown improved corrosion resistance in comparison with the other combinations.
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Further increase in reinforcement did not show significant improvement because of reinforcement floating on the metal and removed as dross.
Acknowledgement My Sincere thanks are due to my supervisor Dr. P. Rajendra Prasad, for the valuable guidance offered during every stage of my research work. I thank Principal, RLJIT and the management of R. L. Jalappa Institute of technology for the support, encouragement and facilities provided at the institute. References [1] [2] [3] [4] [5] [6]
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Hanumanthe Gowda.,et.al. / Materials Today: Proceedings 4 (2017) 10870–10878
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